Second peak in the far eastern Pacific sea surface temperature anomaly following strong El Niño events

eastern Pacific sea surface temperature anomaly (SSTa) associated with El Niño usually peaks in December, January, and February, and decays in the ensuing months; sometimes, however, after a strong El Niño, a second peak in SSTa is observed in the far eastern equatorial Pacific. It is found that an enhanced westerly wind stress anomaly over the equatorial Pacific basin, usually associated with a meridional swing of South Pacific Convergence Zone (SPCZ), precedes the occurrence of the second peak. As the equatorial thermocline slope balances with the zonally integrated zonal-wind stress, the westerly wind stress anomaly induces deepened thermocline and suppresses upwelling in the eastern Pacific for the double-peak cases. On the other hand, enhanced latent heat release and reduced shortwave radiation cause a pause in warming between the two peaks. As a result, a strong El Niño, usually accompanied by a zonal SPCZ, exhibits distinct double-peak characteristics.